'This Week' Transcript: Sen. Bernie Sanders and Gov. Bobby Jindal

— -- THIS IS A RUSH TRANSCRIPT.

ANNOUNCER: Starting right now on ABC's THIS WEEK, Trump's new targets -- "The Donald" trashing a top Clinton aide.

(BEGIN VIDEO CLIP)

DONALD TRUMP (R), PRESIDENTIAL CANDIDATE: She's married to Anthony Weiner, who's (INAUDIBLE).

(END VIDEO CLIP)

UNIDENTIFIED MALE: Tangling with the media.

(BEGIN VIDEO CLIP)

TRUMP: Sit down. Sit down.

(END VIDEO CLIP)

UNIDENTIFIED MALE: And this morning, the new evidence his hard hits are pushing him to an all-time high.

Hillary's big slide -- the stunning poll out just now revealing Bernie Sanders is surging.

Can he grab Hillary's lead?

Sanders is here live.

And a split verdict.

(BEGIN VIDEO CLIP)

UNIDENTIFIED FEMALE: He did not get freedom.

(END VIDEO CLIP)

UNIDENTIFIED MALE: The new reaction to the jury's decision in that prep school sexual assault case.

From ABC News, THIS WEEK WITH GEORGE STEPHANOPOULOS begins now.

MARTHA RADDATZ, HOST: Good morning. I'm Martha Raddatz.

We begin with that shake-up in the 2016 race. A brand new poll coming in overnight from the critical state of Iowa, showing Senator Bernie Sanders closing in on Hillary Clinton. While on the Republican side, Donald Trump is still soaring.

It's your voice, your vote. And let's take a look at those numbers.

Among Republicans, Trump leads, followed by another outsider, Dr. Ben Carson. Then nobody else breaks double digits. Ted Cruz and Scott Walker are tied for third, but trailing far behind Trump.

The biggest surprise is among Democrats. Clinton's lead now down to single digits, just 7 points ahead of Sanders. It's the first time she's dropped below 50 percent in "The Des Moines Register"/Bloomberg Poll this year.

We're taking on every twist and turn in the 2016 race this morning.

And Bernie Sanders is standing by live to weigh in.

First, ABC's Jon Karl on the dramatic difference between the leading candidates right now.

(BEGIN VIDEOTAPE)

JONATHAN KARL, ABC NEWS CORRESPONDENT (voice-over): It's the tale of two frontrunners. For one, the best of times. For the other, well, if it isn't the worst, it's getting there. The Republican establishment fretting their frontrunner is too strong, could actually win. The Democratic establishment fretting theirs is too weak and could actually lose.

While Hillary Clinton has a comfortable lead in national polls, she's already trailing a 74-year-old self-described socialist in New Hampshire. And now, Bernie Sanders is surging in Iowa, as well, despite yet another mea culpa over her private home email server...

HILLARY CLINTON (D), PRESIDENTIAL CANDIDATE: I should have used two emails, one personal, one for work. And I take responsibility for that decision.

KARL: Doubts over her email account still under investigation by the FBI, are taking a toll. Sixty-one percent of voters now say she's untrustworthy, while some Democrats are urging Vice President Biden to jump in, handing out these candy bars at this week's DNC meeting.

Trump, meanwhile, is having the time of his life, riding high in the early states, riding high nationally, seemingly riding high everywhere. Top Republicans are worried he's alienating key voting groups. Jeb Bush even making his own trip to the border to trash Trump's plan to deport undocumented immigrants.

JEB BUSH (R), PRESIDENTIAL CANDIDATE: His proposal is unrealistic. It will cost hundreds of billions of dollars. It will violate people's civil liberties.